Advanced underwater robots discover deep-sea squid that lay giant eggs

The deep sea is the largest living space on Earth, but many animals and habitats deep below the ocean’s surface remain shrouded in mystery. MBARI’s advanced underwater robots, including remotely operated vehicles (ROVs), help explore life in the deep ocean.

During an expedition to the Gulf of California, Mexico in 2015, MBARI’s ROV Doc Ricketts encountered a mother squid holding a cluster of eggs. MBARI researchers had previously observed deep-sea squid tilting their eggs, but this observation was surprising because the eggs were twice the size of other languishing deep-sea squid eggs.

A team of researchers from MBARI, GEOMAR’s Helmholtz Center for Ocean Research Kiel and the University of South Florida carefully reviewed the ROV footage and examined samples of similar-looking squid collected on previous expeditions to the Gulf of California.

The team found that this individual likely represents an unknown species in the family Gonatidae and a species that lays giant eggs. The researchers shared their findings in Ecology.

“Squids play an important role in the ocean – they are wild predators and a vital food source for many animals, even humans – but we still have a lot to learn about the octopuses that live in the deep sea. Advanced underwater robots are helping us better understand the life of deep-sea squids and revealing fascinating new information about their biology and behavior. Each new observation is another piece of the puzzle,” said Henk-Jan Hoving, a previous MBARI postdoctoral fellow who now leads the deep. – marine biology working group at GEOMAR and was the lead author of this new study.

Scientists still have many unanswered questions about the life of deep-sea squid. For most deep-sea squid, scientists have never observed adult females or their spawned eggs.

While maternal care is common in octopuses, burping has only been observed in a handful of squids. Most squid species leave clusters of eggs attached to the seabed or release neutrally buoyant egg masses containing thousands of eggs that drift in the water column. These reproductive strategies require relatively little effort compared to providing care for the eggs after spawning.

“The strain takes a toll on the mother squid. She won’t eat while carrying the eggs and eventually dies after the eggs hatch. But her sacrifice increases the chances that her offspring will survive. It’s just one of many remarkable adaptations that can help cephalopods survive in the deep sea,” he explained Hoving.

MBARI researchers were the first to observe brooding behavior in deep-sea squid. In 37 years of deep-sea exploration, MBARI’s ROVs have recorded 17 sightings of dusky squid. These include numerous sightings of rutting black-eyed squid (Gonatus onyx) and other squid (Gonatus sp.), species difficult to identify from video alone, as well as the deep-sea squid Bathyteuthis. But the squid observed in the Gulf of California stood out to the researchers.

“The deep sea is the largest living space on Earth, and much remains to be discovered. Our unexpected encounter with giant egg-laying squid caught the attention of everyone in the ship’s control room. This remarkable sighting underscores the diversity of ways in which animals adapt to the unique challenges of life in depths,” said MBARI Senior Scientist Steven Haddock, who was the lead scientist during the expedition that encountered this tense octopus.

By analyzing the video footage and studying similar-looking octopus specimens collected on previous expeditions to the Gulf of California, the research team determined that it was likely an undescribed species in the Gonatidae family.

The research team was intrigued by the large size of this squid’s eggs – approximately 11.6 millimeters (about half an inch) in diameter. Previous observations of Gonatus dusky squids reported eggs half the size, with a maximum diameter of just six millimeters (about a quarter of an inch).

The squid observed in the Gulf of California also laid far fewer eggs than other Gonatus squid. Scientists estimated that she was carrying 30 to 40 eggs, while Gonatus octopuses seen in the past have been known to lay up to 3,000 eggs at a time.

Production of many small eggs is beneficial in environments with limited food and/or high predation. In these environments, a larger number of offspring offers a better chance that at least a few will survive.

Giant eggs may be more beneficial in more stable and predictable conditions in the deep sea, allowing higher investment in fewer offspring that have a better chance of survival. This has been observed in other deep-sea cephalopods, including the deep-sea warty octopus (Graneledone sp.) and the pearl octopus (Muusoctopus robustus).

Extrapolating data reported by other scientists on the rate of egg development, the research team estimated that this new deep-sea squid’s eggs may take one to four years to develop, which is longer than the entire life cycle of most shallow-water squid.

Deep-sea octopuses play a vital role in ocean food webs. They are predators that feed on fish and invertebrates in the middle waters, and in turn are eaten by large fish, sharks, whales, dolphins, seals and seabirds. Deep-sea squid form a large part of the diet of commercially important fish such as tuna, swordfish and sailfish.

Despite their ecological and economic importance, we still know very little about the reproductive biology and natural history of deep-sea squid. MBARI scientists and their collaborators are answering fundamental questions about the biology of deep-sea cephalopods.